1. Field of the Invention
This invention relates to the removal of insoluble solids from aqueous fluids and it relates more particularly, to the removal of these solids from aqueous fluids used to clean a well system or from other operations.
2. Description of the Prior Art
There are many industries faced with disposal of aqueous fluids containing significant amounts of insoluble solids. For example, the processing of mined ores for their mineral values generates large volumes of aqueous fluids loaded with suspended solids in physical environments where their separation under stokes law by settling or flotation is impractical, and thus, the separation must be enhanced by physical and chemical means.
In another valuable industry, the drilling, completion and workover of well systems, large volumes of aqueous fluid can be produced carrying varying amounts of oily material and insoluble solids such as rust, scale, sand, barite, metal carbonates, cement and drilling muds (both water and oil based types). Before a well bore is completed, and especially before brine packer fiuids can be used, the well system (tubing, casing, well bore, well head and flow lines) are cleaned by circulation therethrough of wash water. The wash water may have additives to remove thoroughly the residual insoluble solids from the well system. Reference may be taken to our related patent application Ser. No. 420,140 now U.S. Pat. No. 4,453,598 for an "Improved Drilling Mud Displacement Process" wherein is described a very effective procedure to remove residual insoluble solids from the well systems. The resultant aqueous fluid is the wash water carrying insoluble solids of the aforementioned types and may include soluble material such as sea water, and packer and completion brines.
In some instances, as where slug displacement cleaning procedures are encountered, a very valuable packer brine can become contaminated with insoluble solids. These contaminated brines cannot be used for packer or completion services since the solids will precipitate in time upon the packer, seriously injure the formation by plugging the pore space therein or even of the perforations and channels providing fluid flows between the formations and wellbore. Reference may be taken to our related patent applications Ser. No. 310,653 now (U.S. Pat. No. 4,456,537) and 450,519, filed Oct. 19, 1982 and Dec. 12, 1982, respectively both entitled "Chemically Cleaning Drilling/Completion/Packer Brines" for a procedure to remove insoluble solids from the high density brines formed of the sodium, calcium and zinc salts with chloride or bromide. These brines must be cleaned so that the residual insoluble solids are less than 5 microns in maximum dimension and are less than about 0.02% by weight in the brine.
The treatment of aqueous fluids to remove insoluble solids is especially difficult on offshore rigs because of the limited space and equipment that is available and capable of effective solids removal.
If the amount of solids in the aqueous fluid were small in amount, the rig equipment may be used for their removal usually in a stepwise flow pattern through conventional rig filters. However, the costs of manpower and rig time in filtering the fluid is usually prohibitive (e.g., $100,000 per each work shift) unless the solids are (1) less than 0.01% of the well fluid, (2) granular, and (3) not gelatinous as is usually the case with bentonite mud contamination.
The use of conventional rig filters is impractical on other than very low solid contents in the aqueous fluid. Further, rig time in equipment and manpower is restricted and available only for critical operations, namely optimum drilling of the well bore. As a result, aqueous fluid with large solids contamination must be either discarded or returned to some facility for purification. If the aqueous fluid is to be reused, it must be treated to remove the solids in most cases. Usually, the aqueous fluid cannot be discarded or disposed in most regions with its content of insoluble solids and oily material because of the EPA and State pollution abatement laws.
The rig equipment is not usually universal in being able to remove the insoluble solids from the aqueous fluid by filtration, settling (decanting) and flotation processes. In most instances, the available rig equipment would be able to perform one of these solids separation functions. Unhappily, the operator responsible for solids removal from the aqueous fluid only has last minute notice of which separation function will be available in the rig equipment.
The present invention is a process that provides for removal of insoluble solids from aqueous fluid using a minimum of chemicals and simple procedural steps; and the solids removal can be selectively arranged for settling, flotation or filtration functions.